While the improved valves according to the present invention have been specifically designed for gas systems, in which they must meet preset stringent requirements, such as a high resistance against outer high temperatures, i.e. in fire conditions, they can also be used for any liquid fluids.
The inventor believes that of the above prior valves, the valve disclosed in the Italian Utility Model No. 209,019, corresponding to the U.S. Pat. No. 4,714,236, represents the most pertinent status of the art.
While ball valves for liquids can be made from metals or plastic materials, ball valves for gases can be exclusively made from metal materials, since a plastic material cannot resist against, for example, the high outer temperatures of a fire event.
Even if the ball shutter and screw elements of plastic material ball valves are conventionally made as a plastic material single piece, to which the control member, such as a knob, can be fixedly coupled, it should be apparent that the above mentioned single-piece ball shutter-rod unit, as well as the valve body, and the related molding and assembling processes, cannot be merely adopted when using a metal, such as brass instead of a plastic material.
Thus, in the following disclosure exclusively metal valves will be considered.
Since the gas valves must meet technical requirements set by very stringent regulations, it would be moreover apparent that these valves must operate in a very reliable manner. On the other hand, it has been found that prior valves could be further improved both operatively and construction-wise.
With reference to FIG. 1, showing the prior art disclosed in the U.S. Pat. No. 4,714,236, a valve 1 comprises a valve body 2, arranged between an inlet fitting 3 and an outlet fitting 4, and a chamber 6 for engaging therein a ball shutter 7, supported between two opposite sealing gaskets 8, which are individually housed in a respective annular recess 9.
As the bottom portion of the valve 6, having a circular shape in a middle horizontal plane thereof, has a substantially spherical configuration, the gaskets 8, on their side facing the chamber 6 inside, circumferentially project cantilever-wise, in a different degree, from their seats. Thus, the compression on the gaskets by the conveyed fluid, i.e. that fluid which is present in the valve, would not be evenly distributed in the circumferential direction and, in a high pressure condition, said gaskets would be deformed with a consequent resistance against a rotary movement of the ball.
Moreover, for lightening the ball shutter, and reduce the shutter material cost, the inside of the shutter 7 is hollowed by turning operations. Thus, this weight reducing process would require a comparatively long operation time and, while allowing to recover the high value metal, would increase the making cost.
With reference again to FIG. 1, the valve control rod or screw is indicated by 11 and is engaged in a seat 13 of the collar 12 of the valve body 2, the screw being clamped by a friction ring or washer 14 and a resilient ring 16, engaged in a contoured slot 17 of the collar 12. The reference numbers 18 and 19 respectively indicating a sealing O-ring and a supporting and flame-breaking gasket, housed in corresponding grooves of the rod 11.
Prior valves are moreover affected by the following drawbacks:
the provision of a comparatively large number of components, such a eleven components for the valve of the U.S. Pat. No. 4,714,236; PA1 the provision of a ball shutter and rod which are removably coupled to one another, thereby requiring two machine tools for making them from a bar material with a consequent increase of the making and assembling cost; PA1 the reduction of the ball weight can be obtained only by a complex and long inner spherical turning of the shutter; PA1 the abutments for limiting the 90.degree. rotary movement of the shutter are formed as lugs on the valve body and co-operate with counter-abutments provided on the control member, for example a knob, thereby if said knobs is loosen or illicitly removed, then the shutter could not be arranged off or on position; PA1 the contoured seat provided in the rod element housing collar increases the machining time and, consequently, the making cost; PA1 the rod coupling means require two discrete components, i.e. a suitably sized locating washer and a clamping resilient ring element.